Follicle stimulating hormone (FSH) is a glycoprotein hormone that plays a major role in fertility. Crystallographic studies of human FSH are aimed at identifying molecular features that are responsible for receptor binding and signal transduction by correlating the structural data with results of site directed mutagenesis. Endo A is an endoglycosidase, an enzyme that releases oligosaccharides from glycoproteins, that is unique because of its transglycosylation properties. Structural characterization of Endo A will provide important insights in the function of the enzyme that will lead to further development of the enzyme as a tool for the production of neoglycoconjugates.